<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>margin 的计算</title>
    <style>
/*<!--  margin的计算， 全正选大， 一正一负相加-->*/
        main{
            width: 10rem;
            height: 10rem;
            margin: 50px;
        }
        main:nth-child(1){
            background-color: cyan;
            margin: 100px;
        }
        main:nth-child(2){
            background-color: purple;
        }
    </style>
</head>
<body>
<main></main>
<main></main>
</body>
</html>
